The present invention relates to an improved method for the preparation of a polarizing film or sheet or, more particularly, to a method for the preparation of a polarizing film or sheet based on a polyvinyl alcohol film unidirectionally stretched and treated with iodine.
It is well known that, when stretched unidirectionally, dyed with iodine and then subjected to a stabilizing treatment, films of a polyvinyl alcohol exhibit polarizing effect. These polyvinyl alcohol based polarizing films have several problems that the stretched polyvinyl alcohol films are very fragile so that they must be handled with utmost care in the iodine treatment and the stabilization treatment and the thus obtained polarizing film must be adhesively bonded to a reinforcing substrate as soon as possible to avoid possible break of the film though not always with satisfactory results due to the break of the film in the step of bonding with an adhesive agent.
Accordingly, it has long been desired to develop a novel method for the preparation of a polarizing film or sheet with a polyvinyl alcohol as the base material without the above described problems.